NUTRITIONAL-REQUIREMENTS OF THE CORNEAL EPITHELIUM AND ANTERIOR STROMA - CLINICAL FINDINGS

PURPOSE. To monitor the health of the epithelium and the anterior stro ma when porous membranes are implanted into the feline cornea and to d etermine membrane diffusivity characteristics needed to maintain corne al integrity. METHODS. Filtration membranes in a range of effective po re sizes of less than 15 nm (groups 1 and 2, n = 11): 25 nm (group 3, n = 8), 50 nm (group 4, n = 16), and 100 nm (group 5, n = 15) were imp lanted into an interlamellar corneal pocket of the stroma. The implant ed membranes ranged in thickness from 6 nm to 15 nm and were between 8 mm and 12 mm in diameter. Animals were monitored for clinical signs o f intolerance to the implants. RESULTS. At 1 month, thinning and ulcer ation had occurred in the epithelium and the anterior stroma of all an imals in groups 1 and 2; epithelial changes, anterior stromal thinning , and ulceration had developed in 75% of animals of group 3; 50% of an imals showed vascularization and only 7% showed epithelial degeneratio n in group 4; and local anterior stromal thinning was observed in 7% o f animals in group 5, indicating clinical acceptance of the implanted membrane. Ln the long term (greater than 50 days), 30% and 73% of the group 4 and 5 corneas, respectively, were clinically quiet. Analysis o f the failure times indicated an inverse relation between failure rate and pore size: less than 15 nm > 25 nm > 50 nm > 100 nm. The differen ce between the 100-nm and 50-nm membranes was significant (P = 0.03). CONCLUSIONS. A corneal implant must have a porosity greater than that provided by 50-nm membranes. The 100-nm membranes used in this study e stablish the porosity needed to satisfy tile nutritional requirements of the cornea.